A magnetron oscillator is a high-efficiency and high-powered electromagnetic wave generating device that converts electric energy of an electron beam generated in a high vacuum where there is a crossed field where an electric field and a magnetic field are perpendicularly applied to high-powered electromagnetic wave energy and radiates the high-powered electromagnetic wave energy.
The magnetron oscillator was first designed in the 1930s and started to be researched and developed in earnest in the UK and USA for radar applications starting from World War II. Currently, the magnetron oscillator is widely used in industrial, defense, medical, environmental, scientific, and energy fields using characteristics of the magnetron oscillator.
The magnetron oscillator may include a cathode generating the electron beam and a resonator having a constant operating frequency, and an output unit having an antenna structure for radiating the electromagnetic wave generated in the resonator to the outside. More specifically, the electron beam generated in the cathode rotates in each direction according to the Lorentz force by the electric field generated by a voltage applied between the cathode and an anode and the magnetic field applied in an axial direction. In this case, the rotating electron beam resonates at a specific frequency with the resonator and is spatially gathered through the resonance to have an AC component. The electromagnetic wave having an operating frequency is generated in the resonator by the AC component of the electron beam and the generated electromagnetic wave is radiated to the outside through an output section constituted by an antenna. A frequency of the electromagnetic wave generated from the magnetron oscillator can generate the electromagnetic wave from a microwave band to the terahertz wave band according to a condition causing the resonance.
As an example, a high-powered magnetron is used in combination with a linear accelerator (LINAC) to accelerate the electron beam by supplying high output RF in the linear accelerator. As described above, in this case, the resonance frequency of the linear accelerator and the RF of the magnetron to be applied need to be matched in order to accelerate the maximum electron beam in the connected linear accelerator. To this end, in the high-powered magnetron, in most cases, a tuning structure is installed on one side of the high-powered magnetron and the frequency oscillated from the magnetron is adjusted by using a change in electric field depending on a gap distance in the installed tuning structure. In this case, the power increases with the increase of the frequency as a gap increases for frequency variation, but when the gap is out of a predetermined distance, the oscillation becomes unstable rapidly. Therefore, the currently used high-powered magnetron has a limit in the maximum frequency variable width, such as using a frequency variable width within approximately 10 MHz to maintain stable oscillation.